1. Field of the Invention
This invention relates to an ink cartridge. More particularly, this invention relates to an ink cartridge provided with a pressure controller so as to precisely control ink pressure therein.
2. Description of Prior Art
In the field of the printing device, xe2x80x9cDrop-On-Demandxe2x80x9d is a general control method used to control the flow rate of the ink dropping on the printing surface. For example, thermal bubble type printhead and piezoelectric type printhead are two classic outputting devices designed by xe2x80x9cDrop-On-Demandxe2x80x9d.
Thermal bubble type printhead has a film resistor. The ink droplet is immediately vaporized and the expansion effect is generated as the film resistor is energized, and then parts of ink droplet is jetted out off the nozzle, and finally dropping on the printing surface. The thermal bubble type printhead controlled by the xe2x80x9cDrop-On-Demandxe2x80x9d will cause the ink oozing through the nozzle if it is not taken a control mechanismxe2x80x94to generate a predetermined negative pressure in the ink cartridge while the printing procedure is stopped.
Some of ink cartridges are provided with a xe2x80x9cregulatorxe2x80x9d, disposed in the ink container to generate negative pressure therein. In general, a regulator such as air bag is used to change the volume of the ink container by expansion or contraction so that the adequate negative pressure can be generated.
However, the volume in the ink container cannot be further increased once the maximum degree of the expansible air bag is limited. When this occurs the air bag cannot be further expanded and the ink stored in the container continues draining out, the negative pressure is relatively increased over the predetermined value. Then, the ink supply of the printhead will be abnormally terminated and then the remaining ink cannot be used.
For solving the above problem, some printing devices are applied with xe2x80x9cbubble generatorxe2x80x9d to control the negative pressure in the cartridge. The bubble generator is provided with a designed through hole which is connected the inner space of cartridge to the ambient atmosphere and used to generate xe2x80x9cliquid sealxe2x80x9d with capillary forces so as to keep the ink remaining in the cartridge.
When the negative pressure is raising up to a preset value and it is larger than the capillary forces, the atmospheric air from the ambient atmosphere is quickly sucked into the ink cartridge via the through hole and scrubbed into bubbles dispersing in the ink. Then, the negative pressure can be immediately decreased by the generation of these bubbles, and then the liquid seal can be rebuild as the negative pressure is smaller than the capillary forces.
There are several crucial functions for the bubble generator. First, the negative pressure has to be precisely controlled as the bubbles are generated. Second, the variation of negative pressure in the cartridge has to be precisely controlled within a predetermined range, and the generation of the bubbles has to be terminated when the negative pressure is lower to a predetermined value. Third, xe2x80x9cself-wetting capabilityxe2x80x9d has to be provided. As the ink is about to be used up or the position of the cartridge is altered, for example, resulting in the bubble generator is not merged in the ink, the self-wetting capability of the bubble generator can effectively prevent the ambient air from entering into the cartridge.
U.S. Pat. No. 5,526,030 discloses the bubble generator provided with a through hole and a packing member. Several ribs are protruded from the inner wall of the through hole and used to position the packing member within the through hole. The packing member cannot be moved or rotated within the through hole and the gaps between the packing member and the inner wall are used to generate bubbles. The ""030 case further comprises a liquid sealing device and is configured with the ability of self-wetting. For generating desirable negative in the ink pen, the annular orifice between the fixed sphere and the inside of the boss must be precisely calculated and manufactured. This increases the production cost and difficulty of fabricating the device.
To solve the above problem, the primary object of this invention is to provide an ink cartridge comprising a pressure controller so as to adjust the inner pressure therein by atmospheric pressure while the ink stored in the ink cartridge is gradually drained off. The ink cartridge has a container used to store ink with negative pressure therein. At least one through hole is formed on the container and used to connect to the atmosphere, and at least one recess is formed on the inner wall of the through hole. The pressure controller has a plug movably disposed on the through hole and the recess. The recess is designed to regulate the pressure difference between the ink in the container and the atmosphere, and the plug can be automatically shifted to enlarge the clearance between the plug and the through hole while the ink stored in the ink cartridge is gradually drained off.